Article: Brachial plate structure in the brachiopod family Pentameridae

The pentameracean family Pentameridae is characterized by long, rod-like or blade-like brachial processes, buttressed at their posterior end by high plates extending forward far enough to enclose the brachial muscle field. Variations in the internal structure of the brachial valve, combined with changes in external form of the shell, permit the family to be divided into three subfamilies: Pentamerinae, Gypidulinae, and Clorindinae. The articulating muscles in the pedicle valve were seated in the trough-like spondylium which has remained relatively stable and unchanged throughout the history of the family. The Pentameridae range from the Late Ordovician into the Late Devonian.A new genus Clorindella, type species C. areyi, is proposed for costate Clorindinae with a brachial cruralium. The genus Pentameroides Schuchert and Cooper, 1931, is redescribed and the subfamily Pentatneroidinae Amsden, 1953, is abandoned. Pentamerella Hall, 1867, is redescribed on the basis of Hall's type specimens of P. arata. Additional information is furnished on the internal structure of Conchidium munsteri St. Joseph, 1938, based on topotype material from Zone 5b of Norway.